The present invention is directed to methods of producing non-aqueous dispersions of photosensitive polymeric microparticles.
Photosensitive materials demonstrate a response to electromagnetic radiation, including infrared, visible and ultraviolet radiation as well as light amplification by stimulated emission or laser. This response can be a type of luminescence in which visible radiation is emitted by a photosensitive material after exposure, e.g., fluorescent and phosphorescent materials; in which there is a change in the wavelength of the electromagnetic radiation passing through the material, e.g., non-linear optical materials; or in which there is a reversible change in color, e.g., photochromic materials.
Aqueous dispersions of photosensitive microparticles, and waterborne film-forming compositions containing them, can demonstrate several disadvantages. For example, waterborne film-forming compositions tend to generate foam during formulation, far more so than solventborne compositions. Foaming can make application difficult. Expensive humidity controls are often needed for application of waterborne film-forming compositions, since relative humidity can affect flow properties and drying rates of a coating. Choices for adjuvant organic solvents can be limited in waterborne compositions because of evaporation rates and poor compatibility with the aqueous medium. Also, the high surface tension of water can result in difficult wetting of certain substrates. Production equipment which contacts waterborne compositions need to be corrosion resistant. This usually involves using plastic or expensive stainless steel in the production environment. Waterborne compositions also can be difficult to render acid free due to the stabilization mechanism of acid in water. The use of materials comprised of water-sensitive functional groups, such as epoxy groups, can be problematic in waterborne coatings because appearance problems such as blushing in humid environments can develop. Microorganism growth also can be a problem in waterborne compositions.
There are known products that utilize photosensitive materials, e.g., optical elements such as optical memory elements and display elements. Although products incorporating core/shell microparticles that demonstrate photosensitive properties are known, it is desirable to provide non-aqueous products in which the properties of the photosensitive materials in the microparticles can be controlled, thereby avoiding the drawbacks of waterborne compositions. It is also desirable to control product properties such as hardness or abrasion resistance, without adversely affecting the properties of the photosensitive materials which comprise the products.